1. Field of the Invention
This invention relates to a method for producing swellable fluorine mica having the property of being swelled by readily incorporating moisture in the air into its interlayer site of crystals at room temperature or non-swellable mica.
2. Background Information
This kind of fluorine mica has been prepared in the prior art according to the so-called melting method in which silica, magnesia, alumina and a fluoride are used as the starting material, melted at a high temperature of 1,300.degree. C. or higher and cooled gradually, or according to the so-called solid reaction method in which a mixture of feldspar, olivine, quartz and a fluoride is subjected to the reaction at 1,000.degree. C. or higher for 2 to 24 hours. However, such methods of the prior art had the drawbacks that the reaction temperature was too high, that the reaction time was too long, etc.
Accordingly, in Japanese Patent Publication No. 1215/1984, there has been known a method in which fluorine mica represented by MF.3MgO.4SiO.sub.2 (wherein M represents K, Na or Li) is produced by adding 15 to 25% by weight of an alkali fluoride powder to talc and heating the mixture at 800.degree. to 1,200.degree. C. However, for making the reaction time within one hour, the temperature must be still maintained at a high temperature of 1,000.degree. C. or higher, and in a practical aspect, it has been desired to further lower the reaction temperature and shorten the maintenance time.
Further, in Japanese Unexamined Patent Publication No. 201616/1986, there is disclosed a method for producing swellable mica represented by 2LiF.3MgO.4SiO.sub.2 by adding 15% by weight of LiF to talc and heating the mixture at 650.degree. to 780.degree. C. However, it has been desired to have a method for obtaining a product substantially comparable in quality with swellable mica obtained by use of LiF as the starting material without using expensive LiF or using it in an amount as small as possible.